1. Field of the Invention
The present invention relates to a mobile communication system. More particularly, the present invention relates to a method and an apparatus for establishing a call in a mobile switching center (MSC).
2. Description of the Related Art
Typically in a conventional mobile communication system, a procedure for setting a speech path based on radio network resources of the mobile station is required in order to establish a call for providing the service between mobile stations. Such a procedure for establishing the call should follow only a standardized procedure. Unlike a synchronous mobile communication system such as that employed in Korea, an asynchronous mobile communication system, which is some times called a “European Type” system, defines a procedure for establishing the call requiring two steps, that is, one step for setting up a Radio Resource Control (RRC) connection path for transmitting control information, and another step for setting up a service connection path for transmitting user traffics. Accordingly, the calling mobile station and the called mobile station perform the step for setting up the RRC connection path and the step for setting the user traffics connection, respectively.
FIG. 1 illustrates a structure of a conventional asynchronous mobile communication system. In FIG. 1, the system comprises a base station 105 for setting up an RRC connection path connected with a calling mobile station 100, a radio network controller (RNC) 115 for controlling the RRC connection path via the base station 105, a base station 130 for setting RRC connection path connected with a called mobile station 135, a radio network controller (RNC) 125 for controlling the RRC connection path through the base station 130, and a Mobile Switching Center (MSC) 120 for providing service connections between the RNCs 115 and 125. According to such a structure in the conventional asynchronous mobile communication system mentioned above, the users can communicate with each other through the mobile stations 100 and 135.
Each of the base stations 105, 110 and 130 has at least a transceiver capable of performing wireless communication with the mobile stations 100 and 135. The RNCs 115 and 125 control the base stations 105, 110 and 130, and exchange messages for setting up RRC connection path and the service connection path with the base stations 105, 110 and 130 and the MSC 120.
FIG. 2 illustrates a process for establishing a call in a conventional mobile communication system shown in FIG. 1. In FIG. 2, for simplicity and clarification to further understand the prior art, procedures for establishing the calls between the calling and the called stations and the base stations are omitted. At step 205, the calling mobile station 100 performs Radio Resource Control (RRC) connection setup between the base station and the calling mobile station 100 in accordance with control of the RNC 115. At step 210, if the RNC 115 transmits a service request message to the MSC 120, the MSC 120 receives the service request message. The service request message has been sent from the mobile station to the network to initiate a call establishment originated by the calling mobile station. Also, the service request message comprises a bearer capability. At step 215, the MSC transmits an incoming call request message to the RNC 125 which covers the called mobile station 135 located therein. Next at step 220, the RNC 125 sets up RRC connection path between the called mobile station 135 and the base station. Then at step 225, the RNC 125 transfers, to the MSC 120, the service acceptance message indicating that the called mobile station can accept the service requested by the calling mobile station. The service acceptance message also comprises the bearer capability. Next, at step 230, the MSC 120 which has received the service acceptance message transmits, to the RNC 115, a service connection path setup request message for transferring user traffics between the mobile stations and the base stations based on the types of the services. Then, at step 235, the RNC 115 sets up the service connection path for transferring the user traffics between the mobile stations and the base stations according to the setup request message of the MSC 120. Also at step 240, the RNC 115 sends a setup response message of the service connection path to the MSC 120. Then, at step 245, the MSC 120 sends the setup request of the service connection path to the RNC 125. Next, at step 250, the RNC 125 sets up the service connection path between the mobile terminal 135 and the MSC 120. Then at step 255, the RNC 125 provides a service connection path setup response, and completes all the process of the call setup. As a result, if the called mobile terminal gives a response to the ring caused by the call, then speaking or communication between the calling and the called mobile stations can be made through the established service connection path.
By the way, in process for RRC connection setup at step 220, if there is no response from the called mobile terminal, after a certain time period has elapsed, the MSC 120 sets up a service connection path connected with the calling mobile station in order to transmit service-unavailable notice broadcast.
Such a conventional process for establishing a service connection path setup can be classified largely into 4 steps including a first step for an RRC connection setup of the calling mobile station at step 205, a second step for an RRC connection setup of the called mobile station at step 220, a third step for a service connection path setup of the calling mobile station at step 235 and a fourth step for a service connection path setup of the called mobile station at step 250. The 4 steps mentioned above are performed sequentially according to the process flow. Therefore, the process for performing the service connection path setups of both the calling and the called mobile stations is a time-consuming procedure.